1. Field of the Invention
The present invention pertains to a method for the production of a noise-reducing covering for the inside fittings of passenger compartments of vehicles with carpet covering on the passenger side, which incorporates a carpet surface layer and a carpet subsurface layer especially consisting of foamed plastic, with an acoustic insulation composite made up of at least one dense layer turned toward the carpet covering working as the solid mass of an acoustic spongy mass composite and a spongy mass layer turned toward a vibrating bottom part of the automobile body, working as spongy mass layer having sound-damping quality and being the other part of the acoustic spongy mass composite, and also a noise-reducing covering manufactured according to this method.
Such methods and coverings are used mainly in the field of automobile construction, where coverings that are not only decorative but also functional are used for the inside fittings of vehicles. Especially recently, coverings are being used with which the noise transmission level can be appreciably reduced in the passenger compartment in order to increase the degree of comfort. On that account, the modern automobile industry shows great interest in features leading to the effective reduction of among other things the noise level generated by motor, exhaust or tire noises inside vehicle passenger compartments.
2. Description of the Prior Art
Conventional measures for reducing the noise level are generally carried out in two steps. In the first step the noise-transmitting and noise-generating auto body parts are coated with bituminous coatings and are stiffened. In the second step a sound insulation composite is applied as an acoustic spongy mass composite, onto which, is then applied a decorative carpet. Such multiple-layer composite coverings on the one hand dampen the street noises by the mass effect as well as by the reinforcement produced by the dense bituminous layer coated thereon, for instance in the wheel wells, and also dampen the body sound produced by vibration of the auto body parts. The carpet coverings which are either glued on or simply placed thereon generally have another sound-absorbing backing foam layer, in order to further reduce the noise level in the vehicle passenger compartment. Such multiple-layer composite coverings are characterized by their relatively effective general sound-damping and body sound-damping properties and can be adapted relatively simply by any desired selection of carpet coverings to obtain the desired decorative effect. However these multiple-layer composite coverings are often undesirably thick, have a voluminous and complicated method of manufacture and are extremely problematical in handling.
An adhesive insulation composite is described in European Patent A-253,376, in which a first coating is applied to the bottom layer and said first coating supports a multiple-layer insulation working as acoustic spongy mass composite. An uncoupler layer consisting of non-rigid elastic, predominantly open-pore material, is applied to this insulation layer or its dense integral sublayer, and a carpet covering consisting once again of surface layer and subsurface layer is fastened to the uncoupler layer. This insulation composite indeed is acoustically effective, but for various reasons is not very satisfactory.
On the one hand the construction suggested by European Patent A-253,376 yields a composite covering which must be produced in a special step during automobile manufacture, where the work must be done in as little space as possible, and this construction is of unacceptably great height. On the other hand the uncoupler layer disclosed in the European Patent A-253,376 reduces the non-slip quality of the entire covering and thus produces a sense of instability and insecurity for the passenger. One further considerable drawback of the noise-transmission-reducing covering disclosed in European Patent A-253,376 lies in the moisture- and dampness- suction capability inherent in any open-pore material, whereupon these coverings become quickly contaminated and rapidly lose their desirable properties. Such contaminated coverings are subject to undesirable decomposition processes to troublesome evaporation which significantly reduces its useful service life. In sum, the method for production of such an adhesive insulation composite and the resulting article are costly and impractical.
European Patent A-104,357 describes a multiple-layer sound-damping covering which is adhesively attached to the bottom plate of a vehicle and consists essentially of a first resilient absorption layer, a dense porous layer, a second comparatively rigid absorption layer and a decorative cover layer. The objective of this sound-damping covering is to improve the damping of noise transmission reflected from the auto body parts into the inside of the vehicle, especially noise below 1 kHz. The layer construction described in European Patent A-104,357 requires a costly method of manufacture and is therefore not very commercially attractive. These sound-damping coverings are usually manufactured of foam material. Therefore the latter must have a closed cover layer in order to prevent the flow of the foam backing through the pores of the carpet layer to the visible side of the decorative cover layer. These sound-damping coverings are not suitable for absorption of the sound field found inside the vehicle passenger compartment.